Relatively low number of infections, deaths reported last year.

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WEDNESDAY, Sept. 5 2012 (MedPage
Today) — The 2011-2012 influenza season peaked late,
with low rates of outpatient visits, hospitalizations, and deaths, according to
an update from the CDC.

Of almost 170,000 possible influenza specimens tested by the CDC
between October 2011 and May 2012, 13 percent were positive, the agency
reported in an Morbidity and Mortality Weekly Report
published in the Sept. 5 issue of the Journal of the American Medical
Association.

Influenza A viral strains predominated, accounting for 86 percent of
cases, while 14 percent were influenza B viruses. Three-quarters of the
influenza A viruses were H3N2 strains, while the remainder were pH1N1
viruses.

Disease activity peaked late, with the largest number of A strains
being reported during the week of March 17, and most B strains being identified
during the week of April 21.

The highest level of outpatient visits for influenza took place during
the week of March 17, with a rate of 2.4 percent.

In contrast, during the previous year, the highest level of 4.5
percent was seen in early February, while in the 2009 pandemic the rate reached
7.7 percent in late October.

There were 2,356 hospitalizations for influenza between October 2011
and April 2012, with the highest cumulative rates per 100,000 being seen in
older individuals:

Ages 0 to 4 years: 14.2

5 to 17 years: 4.2

18 to 49 years: 4.1

50 to 64: 8.5

65 and older: 30.4

By comparison, hospitalization rates among patients younger than 4
years in other recent seasons have ranged from 35.5 to 72.8 per 100,000, while
rates for those older than 65 ranged from 13.5 to 65.9 per 100,000.

Adult hospitalizations during the 2011-2012 season were most commonly
associated with underlying chronic pulmonary disease in 42 percent, heart
disease in 37 percent, and metabolic disease in 34 percent.

Almost half of children had no underlying chronic disease, while about
20 percent had reactive airway disease.

Adult deaths exceeded the epidemic threshold of 1.6 standard
deviations above baseline for the season only during the week of Jan. 21, at
which time mortality peaked at 7.9 percent.

In recent years, peak percentages for mortality ranged from 7.9
percent to 9.1 percent, during 3 to 13 consecutive weeks.

During the 2011-2012 season there were 26 influenza-related pediatric
deaths, compared with 122 in the previous season and 348 during the 2009
pandemic.

Influenza A H3N2 strains were most commonly seen in the Midwest, while
pH1N1 strains occurred with the greatest frequency in the South and
West.

Influenza B was reported most often in the Northwest.

There also were 13 cases of swine-derived influenza, 12 in children,
with all being H3N2 strains carrying a pH1N1 M gene. Half of these cases
reported no contact with pigs.

Two other unusual swine-origin H1N1 strains also were reported. All 15
swine-related cases recovered from the illness.

Most cases of both influenza A and B were the antigenic types found in
the 2011-2012 Northern Hemisphere influenza vaccine, which included
A/California/7/2009-like, A/Perth/16/2009-like, and
B/Brisbane/60/2008-like.

Most strains were sensitive to oseltamivir (Tamiflu) and zanamivir
(Relenza), with no resistance to either drug being identified among H3N2
strains.

Among the pH1N1 strains, all were sensitive to zanamivir and 1.4
percent were resistant to oseltamivir.

Resistance to amantadine (Symmetrel) and rimantadine (Flumadine)
remains high among circulating influenza A strains; these antivirals are not
currently recommended for influenza.

The FDA's Advisory Committee has recommended that next season's
influenza vaccine include A/California/7/2009-like, A/Victoria/361/2011-like,
and B/Wisconsin/1/2010-like.

All individuals 6 months and older should receive the vaccine each
year, ideally during the autumn, although travelers might consider vaccination
at other times if they are likely to be exposed.

For individuals who develop severe disease or complications, prompt
treatment with oseltamivir or zanamivir should be given, according the the
CDC's Advisory Committee on Immunization Practices.

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